1. Field of the Invention
This invention relates to a new process utilizing new yeast mutants for identifying active FK-506 type immunosuppressants. Specifically disclosed are the new yeast mutants, Saccharomyces cerevisiae YFK093, (Merck Culture Collection No. MY 2088) ATCC No. 74055, containing an fkr3 mutant gene, Saccharomyces cerevisiae YFK 012, (Merck Culture Collection No. MY 2096) ATCC No. 74061, which contains an fkr1 mutant gene, Saccharomyces cerevisiae YFK 014, (Merck Culture Collection No. MY 2097) ATCC No. 74062 and YFK-023-17A (Merck Culture Collection No. MY 2098) ATCC No. 74063, both which contain an fkr2 mutant gene.
2. Brief Description of Disclosures in the Art
In 1983, the US FDA approved cyclosporin, an extremely effective anti-rejection drug that revolutionized the field of organ transplant surgery. The drug acts by inhibiting the body's immune system from mobilizing its vast arsenal of natural protecting agents to reject the transplant's foreign protein.
As effective as the drug is in fighting transplantation rejection, it suffers drawbacks in causing kidney failure, liver damage and ulcers which in many cases can be very severe.
EPO Publication No. 0184162 to Fujisawa, now issued as U.S. Pat. No. 4,894,366 hereby incorporated by reference, describes a new macrolide immunosuppressant FK-506 which is reputed to be 100 times more effective than cyclosporin. The macrolide is produced by fermentation of a particular strain of Streptomyces tsukubaensis. Also described is the closely related macrolide immunosuppressant FK-520, (FK-900520) produced by S. hygroscopicus subsp. yakushimaensis.
In the synthesis of new FK-506 type immunosuppressant analogs, it would be helpful to have a single, convenient diagnostic assay, not involving laboratory animals, to distinguish between those analogs of FK-506 which are agonists and those which are antagonists, i.e. rapamycin. Further, it would be helpful to have a single convenient diagnostic assay to establish the presence of FK-506 type immunosuppressant type activity in a fermentation broth, as opposed to other immunosuppressants; i.e. rapamycin.
Other strains of Saccharomyces cerevisiae and Nerosspora crassa are described in Nature, Vol. 342, pp. 953-955, which are resistant to cyclosporin A and lack detectable cyclophilin binding activity.
However, no description of mutant S. cerevisiae strains which are FK-506 resistant and growth dependent at 37.degree. C., are described in the literature to date.